In certain subterranean formations, it may be desirable to mitigate the flow of fluids through a portion of the subterranean formation that is penetrated by a well.
For example, water production from oil or gas wells is a widespread problem that causes significant economic drawbacks. High water production rates reduce well productivity, increase operating expenditures, and can completely block production from wells. Controlling and eliminating unwanted water influx into oil or gas wells is a major concern of producers.
The water can be the result of a water-producing zone communicating with the oil or gas producing zone by fractures, high-permeability streaks, fissures, vugs, or the like, or it can be caused by a variety of other occurrences which are well known to those skilled in the art such as water coning, water cresting, bottom water, channeling at the well bore, etc. The water may approach from one or more directions (from below, from the sides, or from above). Usually water is produced at the cost of oil or gas recovery. In some circumstances, the ratio of produced water to hydrocarbons may, over time, become sufficiently high that the cost of producing, separating, and disposing of the water may represent a significant economic loss. In severe cases, the water influx becomes so great that the oil or gas production is choked off completely.
In some instances, it may be desirable to control the flow of fluids introduced into the well so that the flow of the fluid into high-permeability portions of the formation is mitigated. In enhanced recovery techniques such as water flooding, an aqueous flood or displacement fluid is injected under pressure into an oil containing subterranean formation by way of one or more injection wells. The flow of the aqueous fluid through the formation displaces oil or gas and drives it to one or more producing wells. However, the aqueous displacement fluid tends to flow through the most permeable zones in the subterranean formation, whereby less permeable zones containing oil or gas are bypassed. This uneven flow of the aqueous displacement fluid through the formation reduces the overall yield of hydrocarbons from the formation. For example, in an injection well, it may be desirable to seal off high-permeability portions of a subterranean formation that otherwise would accept larger portions of an injected treatment fluid. By sealing off the high-permeability portions of the subterranean formation, the injected treatment fluid thus may penetrate less permeable portions of the subterranean formation more effectively.
Heretofore, enhanced recovery problems in a subterranean oil containing formation caused by permeability variations therein have been corrected by reducing the permeability of the subterranean formation flow paths. The techniques utilized to accomplish this reduction in the permeability of high permeability zones are sometimes referred to in the art as “conformance control techniques.” Decreasing excess water production increases the production water/oil ratio (“WOR”), lowering water-handling cost. Conformance control techniques can extend a well's economic life, increasing return on investment. Oil production increases as water production decreases.
A number of methods for controlling water production from subterranean formations have been proposed. For example, methods include processes designed to block pores or channels within a formation by gelation using polymer materials such as polyvinyl alcohol and polyacrylic acid. See, for example, U.S. Pat. Nos. 7,759,292 and 7,563,750, which are incorporated herein by reference. See also, for example, Great Britain Patent No. GB-A-2399364.
Another method that has been proposed involves introducing a barrier, such as a concrete resin, adjacent to the well bore in order to prevent the movement of water into the bore.
More recently, methods to achieve selective water control without the need for zonal isolation techniques comprising hydrophilic polymers have been proposed. It is thought that the hydrophilicity of the polymer affords the desired selectivity. It leads to preferential partition into those channels and pores of the formation having high levels of water without impairment to oil and gas production.
A drawback with the polymers used for water shut-off treatment is that they are partially unstable at high temperatures (i.e., greater than 110° C.). Also, some polymers have a tendency of precipitation at higher temperature in the presence of acid and saturated heavy brines See US Patent Publication No. 2010/0256023, which is incorporated herein by reference. Exposure to such temperatures and/or chemicals can cause the polymers to decompose and/or degrade thereby nullifying their blocking effect. When this occurs, the formation then has to be re-treated which increases the cost further.
Polyacrylamide is commonly used as one of the polymers in water shut-off. Unfortunately, it is potentially damaging the environment because the acrylamide monomer produced on decomposition of polyacrylamide is known to be a nerve toxin.
U.S. Pat. No. 7,325,613 issued Feb. 5, 2008 entitled “Crosslinkable polymer compositions comprising phenols and associated methods” discloses as described in the abstract “Crosslinkable-polymer compositions that comprise a chitosan-based compound and a phenol source, and associated methods, are provided. Various methods of use are also provided,” U.S. Pat. No. 7,325,613 is incorporated by reference in its entirety.
Excessive water production greatly affects the economic life of producing wells. High water cut largely affects the economic life of producing wells and is also responsible for many oilfield-related damage mechanisms, such as scale deposition, fines migration. Though a variety of chemicals are used by the industry to control water production, most of them are not accepted in the regions with strict environmental regulations.
There is a continuing need for improved methods for controlling or blocking water production from certain subterranean zones. It would also be desirable for the methods to avoid risking damage the environment.